It's been my understanding that the (USDM) H22 redline is 7,300, fuel-cut is 7,700, and the tach reads high. I've seen many Prelude drivers post that they hit fuel-cut at an indicated 8,100 on the tach. Also, on many runs on a Dynojet, I've seen that when the tach indicates 8,000 RPM, the Dynojet shows only 7,600 RPM (it reads RPMs off the #1 plug wire). So, anyways, I used the peak-hold on my V-AFC for the first time. I upshifted at a bit before 8K like I always do, and the V-AFC measured a very uncomforting peak value of 7,869 RPM.
My question to you is; does anyone have any indication that the V-AFC also tends to report higher RPMs than actual? The history of my ECU (P13) is a little strange, but it's supposed to be totally stock so I certainly hope I haven't been passing Honda's rev-limit and haven't been slowly destroying my engine for months. (Oh, the engine feels fine and strong as ever though). I have never passed the 8K mark on my tach, and, again, the Dynojet reports 7,600 RPM when my tach indicates 8,000.
Thanks.

 

no, the vafc is dead on. so either your ecu is messed or... or your ecu is messed...

 

I've never owned a VAFC but my understanding is that it reads the accurate RPM's of the motor, whereas Honda/Acura Tach's are off by a few hundred RPM's at or near redline.
HTH
M

 

Almost every single factory tach is off a considerable ammount. For example, '87-'93 Mustang GTs factory tachs read almost 1,000RPMs higher than the actual engine speed. It mostly depends on the quality of the tachometer. As for the V-AFC, I will go ahead and say that the RPM it shows is 100% accurate. A dial sweeper tach(AutoMeter) would be considered primitive compared to a digital tachometer (V-AFC).

 

If you stop and think about it depending on how you hook it up it probably would be off. The factory tach is off because of the translation from the ECU. The engine coil wire goes to ECU which transmits that to the factory tach. So if the VAFC is connected on the outputs on the ECU then it probably would be off as well, but if it were directly to the engine coil then it would be a bit more accurate. When I had my Autometer I had it connected to the ECU for about a week and for that week it read the same as the factory tach. Then we rewired it to the engines coil wire and it was off. The factory went as far as 8400 and the Autometer went to 7200.

 

Yeah, that's what I'm thinking. I don't know if the tach and V-AFC calculate RPMs from the same signal, but the V-AFC also differs from the Dynojet... and the Dynojet has gotta be right as it reads right off of the plug wire.
Thanks for the responses.

 

Hmmm, dyno......hrm......do you have to proper sized tires or was that entered into the dyno was the dyno hooked in some way up to your distributor?

 

Well, since a dyno graphs measurements to specific engine RPMs, it'd better read accurate engine RPMs. A dyno that read RPMs off of the spinning drum would be ridiculous. The Dynojet reads RPM off of the #1 plug wire. On a 4-cylinder 4-stroke engine, each firing of the plug equals 2 crank revolutions.

 

Likewise, the NSX supposedly has an 8000rpm redline cutout...the Apex'i S-AFC on my 1995 NSX-T has peaked at as high as 8275rpm...

Andie

 

the tach and VAFC do run off the same signal, the RPM signal wire is one of the many wire that the VAFC taps into.

 

Or you could wire the V-AFC to the ignition coil.

 

In theory I guess you can but all the wires are at the ECU